Re: The --> "operator" (was: Re: CVS commit: src/sys/uvm)

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

> Date: Tue, 7 Jul 2026 21:11:56 +0200
> From: Roland Illig <roland.illig%gmx.de@localhost>
> 
> Am 07.07.2026 16:08:00 schrieb Taylor R Campbell :
> 
> > This is the best operator in C!  --> is the `goes down to' operator.
> 
> How does it come that this "best operator" is neither mentioned in
> operator(7) nor share/misc/style, and that indent(1) formats it as
> two separate operators? All this looks like you're making things up.

I am, of course, being facetious about --> being an operator in and of
itself: it is a post-decrement operator followed by greater-than.

But, even though it is a little cute, after many years of writing
logic that iterates in reverse over half-open intervals, I came to the
entirely serious conclusion that

	for (i = N; i --> 0;) { ... i ... }

is much more readable and obvious and safe than any of the
alternatives

	for (i = N; i > 0; i--} { ... i - 1 ... }

	for (i = N - 1; i >= 0; i--} { ... i ... }

	for (i = N; i-- > 0;} { ... i ... }

	for (i = N; --i >= 0;} { ... i ... }

as soon as you have spent a moment _once_ to figure out what --> is;
the others all require at least several minutes of thought every time
I look at them to make sure they're doing the right thing, if not
several hours of banging my head against them debugging.

> If you decide that this style is superior, you should adjust the
> aforementioned places (there may be more) and apply this style
> change throughout the whole source tree, for consistency.

I would be happy to do that!  But I realize that, on first reaction,
many people find it a little too cute.  And we don't have every point
of style variation deterministically spelled out in KNF or enforced in
the tree.  For example, we have both `if (!foo)' and `if (! foo)'
throughout the tree already.  And we have three different automated
indentation mechanisms (indent(1), NetBSD.el, and clang-format) that
generally agree on what KNF says but disagree on some things it
doesn't say.